The presence and deteriorating action of micro-organisms on monuments and stone works of art have received considerable attention in the last few years. Knowledge of the microbial populations living on stone materials is the starting point for successful conservation treatment and control. This paper reviews the literature on cyanobacteria and chlorophyta that cause deterioration of stone cultural heritage (outdoor monuments and stone works of art) in European countries of the Mediterranean Basin. Some 45 case studies from 32 scientific papers published between 1976 and 2009 were analysed. Six lithotypes were considered: marble, limestone, travertine, dolomite, sandstone and granite. A wide range of stone monuments in the Mediterranean Basin support considerable colonization of cyanobacteria and chlorophyta, showing notable biodiversity. About 172 taxa have been described by different authors, including 37 genera of cyanobacteria and 48 genera of chlorophyta. The most widespread and commonly reported taxa on the stone cultural heritage in the Mediterranean Basin are, among cyanobacteria, Gloeocapsa, Phormidium and Chroococcus and, among chlorophyta, Chlorella, Stichococcus and Chlorococcum. The results suggest that cyanobacteria and chlorophyta colonize a wide variety of substrata and that this is related primarily to the physical characteristics of the stone surface, microclimate and environmental conditions and secondarily to the lithotype.

The effects of aging on biochar (BC) properties, composition and carbon sequestration are still under debate. This study aimed at illustrating the qualitative alterations of five different BCs aged during a 24-month field experiment located in Southwest Spain. To determine the recalcitrance of each BC, physical fragmentation test, scanning electron microscopy, 13C NMR spectroscopy and CO2-respiration experiments were performed. The physical fragmentation values of all types of BC increased significantly over time at field conditions. FESEM examinations of aged BCs showed collapsed structures and the presence of entrapped soil material and microbial mats into the BC pores. The 13C NMR spectroscopy demonstrated an increase of the relative abundance of O-alkyl C and alkyl C at expenses of aromatic-C in aged BCs. The C losses of all BCs ranged from 27% to 11% of the initial C. In contrast, the nitrogen (N) content of wood-derived BCs significantly increased probably due to the sorption of nitrogen containing compounds into these highly-porous weathered chars. With the exception of that for the sewage sludge-BC, the pH of all aged BCs decreased from >9 to the soil pH, indicating a short lasting of the liming effect caused by BC addition. The respiration experiment revealed that BC recalcitrance was much lower than expected and, within the range of decades. Only wood-derived BCs significantly increased the mean residence time of the slow C pool of the Cambisol by factors between 3.4 and 7.7. Mediterranean climate conditions and the characteristics of the Cambisol used probably accelerated the microbial degradation of BCs.

Volcanic caves are filled with colorful microbial mats on the walls and ceilings. These volcanic caves are found worldwide, and studies are finding vast bacteria diversity within these caves. One group of bacteria that can be abundant in volcanic caves, as well as other caves, is Actinobacteria. As Actinobacteria are valued for their ability to produce a variety of secondary metabolites, rare and novel Actinobacteria are being sought in underexplored environments. The abundance of novel Actinobacteria in volcanic caves makes this environment an excellent location to study these bacteria. Scanning electron microscopy (SEM) from several volcanic caves worldwide revealed diversity in the morphologies present. Spores, coccoid and filamentous cells, many with hair-like or knobby extensions, were some of the microbial structures observed within the microbial mat samples. In addition, the SEM study pointed out that these features figure prominently in both constructive and destructive mineral processes. To further investigate this diversity, we conducted both Sanger sequencing and 454 pyrosequencing of the Actinobacteria in volcanic caves from four locations, two islands in the Azores, Portugal and Hawai`i and New Mexico, USA. This comparison represents one of the largest sequencing efforts of Actinobacteria in volcanic caves to date. The diversity was shown to be dominated by Actinomycetales, but also included several newly described orders, such as Euzebyales, and Gaiellales. Sixty-two percent of the clones from the four locations shared less than 97% similarity to known sequences, and nearly 71% of the clones were singletons, supporting the commonly held belief that volcanic caves are an untapped resource for novel and rare Actinobacteria. The amplicon libraries depicted a wider view of the microbial diversity in Azorean volcanic caves revealing three additional orders, Rubrobacterales, Solirubrobacterales and Coriobacteriales. Studies of microbial ecology in volcanic caves are still very limited. To rectify this deficiency, the results from our study help fill in the gaps in our knowledge of actinobacterial diversity and their potential roles in the volcanic cave ecosystems.